Optical Remote reading of cards, for example for identification, is well known. In general, such cards contain a bar code, such as a code 39, which is read by a remote scanner. Reading at distances of several feet is possible but not easy in many applications. In general, cards containing a bar code are placed in a side window of a vehicle and a scanner placed at the side of a road on which the vehicle travels are used to identify cars, for example at a gate. Since the position of the cards can be controlled (the card is placed at a height at which it always can be read) and the aspect of the card is almost normal to the scanner, such reading can be fairly successful.
The prior art does not read cards placed in the front window of a car, for at least four reasons. One reason is that the position, tilt and aspect (angle of incident light with respect to normal) of the card are less controllable. The second reason is that the use of a laser scanner that points at a drivers eyes, even one in the infrared, is not considered safe. A third reason is that such scanners, especially for measurement at a distance, are expensive. A fourth reason is that there are often stickers or other devices on the windshield of a vehicle, which may be mistaken by a reader for the card to be read.
Flat Retro-reflective sheets are well known. Such reflectors may be of the type utilizing arrays of micro-elements, such as corner reflectors or of the type using beads or other cats-eye type structures to return the light. In general, the acceptance angle (the range of incident angles at which incoming light is retro-reflected) is dependent on the retro-reflector type used. Retro-reflectors are generally imperfect and have a, generally small, spread of angles around the retro angle at which the light is reflected.
Labels utilizing retro-reflector enhanced indicta have been used for providing improved readability of the indicta, for example of indicta placed over them. When the indicta are illuminated, the retro-reflectors selectively reflect the light in the direction of the light source, thereby providing a bright background for the indicta and increased contrast. The prior art also shows the use of colored indicta and the generation of retro-reflector enhanced indicta generated by providing areas of retro-reflectors in the form of an image that is retro-reflected. The indicta/retro-reflectors may be overlayed by other indicta (holograms and engraved patterns are suggested in the art), and/or by coatings that reflect or absorb light at certain wavelengths.
Directed reflectors are also known. A directed reflector is a reflector that reflects incident light at an angle that is offset by a fixed amount from the angle of incidence. One method of generating directed reflectors is by utilizing corner reflectors with faces that are not perpendicular. Reference is made in this regard to “Study of Light Deviation Errors in Triple Mirrors and Tetrahedral Prisms”, Yonder, J., JOSA, V. 48 (7) 1958.